Congrats on completing the jam! This was a fun little game :) I liked the blend of pinball and tower defence. I got to Round 15.
I really liked the canons and shooting yourself out as a pinball and bouncing around. It felt good to squish and roll over a bunch of enemies. The idea of the catapults were cool, but I had difficulty moving my guy around - maybe because I was using keyboard and it would be easier with a gamepad. I would've also liked the catapults to do a slow down or a damaging residue earlier in the game - they didn't do too much damage so i didn't use them and didn't realize they had a slowness upgrade until later because it was blanked out.
The enemies were cute, and felt appropriately intimidating - things ramped up pretty well. At the start of the game I didn't know where the start and the end was - might be good to make that more obvious.
The map design was well done - each tower could show off it's capabilities well.
Otherwise some ideas you could play around with could be building a pinball board and needing to direct your ball around to defend against the waves with maybe more than one goal. I feel like it would be more fun to have to shoot the ball across the map to reload the towers than to stand there and reload. Basically, more movement and more ball shooting would be fun.
Great job!